This disclosure relates to a copolymer formulation for directed self-assembly, methods of manufacture thereof and to articles comprising the same.
Directed self-assembly (DSA) of block copolymers has been identified as a candidate technology to extend the state of current optical lithography. In DSA, small pitch sizes are achieved by directing the self-assembled block copolymer nanodomains to a lithographically patterned substrate. One of the leading methods for DSA involves a chemical pattern to align a lamellar morphology of a block copolymer, such as polystyrene-block-poly(methyl methacrylate), or PS-b-PMMA. The preferred process scheme, shown in FIG. 1, begins by patterning an array of sparse guide stripes (e.g., polystyrene (PS) generally manufactured from a crosslinked polystyrene mat. After the stripes are etched (also termed “etch trimming”) to the proper dimension, the brush polymer is coated over the stripes, baked to induce chemical grafting, and then excess brush polymer is removed by rinsing with a solvent such as propylene glycol methyl ether acetate (PGMEA) to leave a relatively flat substrate with chemical contrast. The substrate is then treated with a block copolymer (e.g. poly(styrene-b-methylmethacrylate)), which after annealing aligns to the substrate to multiply the density of the initial pattern. In this two-step method that involves first applying the brush followed by applying the block copolymer (BCP), the composition of the brush has to be controlled over a fairly tight range in order to achieve good DSA results.
It is therefore desirable to use compositions where the alignment between domains can be easily achieved and where the ranges of the polymers are not so tightly controlled.